The present invention relates to a ring-shaped coupling which is designed to suppress problematic torsional vibration occurring in a drive shaft for example, when joining the forward end of the drive shaft of a marine engine or land engine with the rear end of the drive shaft of the accessory machinery by means of said coupling, or to serve other like purposes.
For example, as shown in FIG. 6, a diesel engine 31 mounted on a ship has the rear end 32 of its drive shaft connected to a reduction gear 34 by means of a flexible coupling 33 and thence to a propeller 35, whereas the forward end 36 of the drive shaft is connected to a speed-increasing gear 38 by means of an air clutch 37 including a ring-shaped coupling and thence to accessory machinery such as a hydraulic pump 39 for winches, etc. and a generator 40.
FIG. 7 schematically illustrates one such ring-shaped coupling which has been in conventional use as a means to suppress torsional vibration of the forward end 36 of the drive shaft as it transmits motive power. This ring-shaped coupling consists of a sleeve 41 which is fitted on the forward end of the drive shaft (not shown in drawings) and fixed in place, a pair of inner rings 43, 43 which are fitted on said sleeve 41 and fixed together in a single body with a bolt 42, a pair of rubber rings 44, 44 whose circumferential inner surfaces are made to adhere by vulcanization to said inner rings 43, 43, a pair of outer rings 45, 45 whose circumferential inner surfaces 45a, 45a, each forming a section of a cone, adhere by vulcanization to the outer circumferential surfaces of said rubber rings 44, 44, a joining ring 47 which is fitted on said outer rings 45, 45 and clamps them together in the axial direction with a bolt 46, a flanged ring 49 which is fitted on the driven shaft (not shown in drawings) and clamped together with said joining ring 47 by a flange 47a and a bolt 48 and fixed in place. The outer circumferential surface of one of said pair of inner rings 43, 43 forms a section of a cone 43a which flares toward the other, whereas the inner circumferential surface of one of said pair of outer rings 45, 45 forms a section of a cone 45a flaring toward the other, and said pair of rubber rings 44, 44 connected by vulcanization to the respective inner and outer rings at said circumferential surfaces are pressed tight against each other in the axial directions by means of said outer rings 45, 45 and said clamping bolt 46, so that torsional vibration of the drive shaft is suppressed by means of the rubber rings 44, 44 and a large torque can be transmitted from the driving shaft to the driven shaft without damage.
The use of the conventional ring-shaped coupling as described above, however, raises various defects and problems because said inner rings 43 and rubber rings 44 consisting each of a pair as follows. To fix the pair of inner rings 43, 43 to the sleeve 41, a flange 41a is extended from the sleeve 41 so that a bolt bore 50 is threaded open through the flange 41a and the inner rings 43, 43 in the axial direction and a clamping bolt 42 is used. In practice this structure raises defects that the moment of inertia on the driving side becomes large so that, while the torsional vibration on the engine side is caused, the manufacturing cost is increased by troublesome machining and increased parts, and the coupling made requires a relatively large space contradictorily to the pursuit of compactness. Also the structure having a pair of inner rings 43, 43 which are clamped with a bolt 42 makes the mechanical strength lower than one solid structure. The rubber rings 44 connected by vulcanization to the inner rings 43 rise apart from the substrates at four edges 44a, which are liable to become the starting points for the breakage of the rubber rings. Furthermore, another problem arises from the vulcanization of the rubber rings, wherein the vulcanization by which a rubber ring 44 is made to adhere to an inner ring 43 starts at the portion of the rubber which is in contact with a heated inner ring 43 and, as the reaction progresses, portions of the rubber not yet cured run into the portions which have been cured by vulcanization reaction, thus relaxing the internal stress in the cured portion, as the vulcanization spreads toward the peripheral area. In this process, when the rubber rings 44, 44 are completely separated in a pair as shown in the drawing, portions of the rubber rings 44, 44 not yet cured can not run mutually into the cured portions, and, as a result, the internal stresses fail to balance in the vulcanized rubber rings, thus raising a problem concerning the efficiency of a coupling.